Rio De Janeiro: The president of Brazil's Senate was put on the defensive with the release of a secretly recorded conversation that reveals him proposing to weaken one of the key tools prosecutors have used to catch politicians and businessmen in a sweeping corruption scandal.

The released transcript and audio, published by the newspaper Folha de S Paulo, appears to feed widespread suspicions that top lawmakers are trying to stifle investigations into billions of dollars in alleged bribes involving the state oil company, Petrobras.

File photo of Renan Calheiros. AP

The conversation shows Senate leader Renan Calheiros suggesting legal changes to bar the use of plea bargains with people who have been arrested. Prosecutors have used such deals, offering lighter sentences to persuade suspects to implicate high-ranking businessmen and politicians, including Calheiros.

"You can't make a plea deal while arrested. That's the first thing," Calheiros allegedly said in a wide-ranging conversation about the Petrobras probe with Sergio Machado, an ex-senator and former head of another state oil company, Transpetro. Machado also is being investigated.

The Supreme Federal Tribunal, Brazil's highest court, is considering seven investigations against Calheiros in the
Petrobras probe. Even so, in the recording, Calheiros said he could "negotiate" with the justices a "transition" from President Dilma Rousseff to Vice President Michel Temer. He didn't provide details in the taped conversation.

Rousseff was suspended by a Senate impeachment vote earlier this month and Temer has taken over as acting president while senators put her on trial within six months.

Calheiros' office issued a statement acknowledging the conversation but insisting that the talks "don't reveal, indicate or suggest any mention or attempt to interfere with" the Petrobras probe.

Later on Wednesday, in another tap obtained and published by Folha, former President

promised Machado that he would help him overcome the Petrobras probe. Sarney, a political heavyweight whose son is environment minister, said he would work to keep the investigation against Machado out of the hands of lower court judge Sergio Moro.

Moro, the lead judge on the Petrobras probe, has gone after many people who don't hold federal elected offices or Cabinet positions. Only the Supreme Federal Tribunal can decide to try the latter.